Laying out mechanical, electrical and plumbing systems in new buildings under construction, or in existing buildings undergoing renovations or additions, is tedious, time consuming, and expensive. Typically, it has required a significant amount of labor to lay out construction points at a construction site for sleeves and hangers on floors and ceilings. This process has required teams of workers that measure and mark the locations of these points, with much of the work being accomplished manually. It will be appreciated that such a process is subject to errors, both from measurement mistakes and from accumulated errors which compound as measurements are made from one intermediate point to the next. Further, building designs and requirements have become more complex, and construction schedules have become tighter, adding to the need to facilitate and simplify the layout process.
Total stations have been used in the past both for outdoor surveying, and for machine control. In a typical surveying application, a total station, positioned at a known location, directs a beam of laser light to a target positioned by a surveyor at a point to be surveyed. The target may include retro reflectors which reflect the beam back to the total station. By measuring the time of flight of the beam, the distance between the total station and the target is determined. By also measuring the direction of the beam from the total station to the target, i.e., the altitude and azimuth angles that define a vector from the total station to the target, the location of the target is precisely determined.
Robotic total stations have been developed that are capable of locating and tracking a target without being attended by an operator. With a robotic total station, the surveyor moves the target around the work site. Servo motors in the robotic total station cause it to rotate toward the target, providing precise angular and distance measurements as the surveyor moves to various locations at the work site. The total station automatically tracks the remote target as it moves, thus providing real-time position data for the target.